Improved method in the manufacture



l Sept. 22, 1936.

. R. ELssNER E1' AL FILAMENT WINDING Filed sept. 24, `1932l (aff ram.

Patented Sept. 22, 1936 UNi'rEDl vfsmTEs PATENT OFFICE IMPROVE METHOD INTHE MANUFACTURE 0F SODIUM ALUMINUM SULPHATE Augustus H. Fiske, Warren,Vand Charles S. Bryan,v

Providence, R. I., assignors to Rumford Chemical Works, Rumford, R. I.,a. corporation of Rhode Island No Drawing. Application March 20, 1935,Serial Y No. 11,978

1,1 claims. (Circ-118)` Our present invention relates to the productionof a sodium aluminum sulphate and particularly to one highly suited asan ingredient for food products, such as baking powders or the like.

It is highly desirable thatv such ingredients be of great purity `andfree from any discolorations. Apure white product therefore has beenlong sought but has been difficult to attain commercially on account ofthe vpresence of impurities in the bauxite source.

IThe usual method heretofore of manufacturing sodium aluminum sulphatehas been in general to dissolve a hydrated oxide of aluminum source insulphuric acid. The usual source Was bauxite and while some depositsprovide this material concentrated to the point where crystallizationvtook place. After crushing and washing, to remove the impure motherliquor, the crystals were heated in a furnace to drive off the water ofcrystallization, and the resultant sodium aluminum sulphate of commercewhile generally satisf factory as to purity was rendered more costlybecause of this long process of manufacture.

We have devseda process by which the procedure can be very materiallyshortened without any sacrifice of purity and a product produced vwhichis of a much desired whiteness.

In accordance with our invention we reduce a bauxite of a very highgrade of purity to a fine powder. This is run into a-mixer with acalculated. amount of so-called salt cake which isa commercial form of amixture of sodium sulphate and acid sodium sulphate. We find thissatisfactory although we may use acid sodium sulphate or sodium sulphatebut as the salt cake is commercially available and of a desirablepurity, we nd it economical to supply the sulphate in this form.` Thesalt cake is reduced to a finely divided state before being run into themixer with the bauxite so .that the two powders become intimately mixedand dispersed with each other. We then add sul-` phuric acid. AThisshould be of 66 Baume strength containing 93.19 percent of I-IzSOl.

Other strengths of sulphuric `:acid maybe used but we have found thisstrength to be satisfactory for economical commercial operation. ATheacid is thoroughlyY mixed with theV previously mixed powders forming'with them a soft cake in the mixer which is readily broken up by thestir'` The premixed 'powders maybe stirred ring arms. into the acid inthe mixer if desired, and this has the advantage of avoiding anytendencytocake and become hard, but the dry ingredients mustu be addedto the acid graduallyand thoroughly stirredin. The thorough premixing ofthe pow-I ders before meeting the acid'is highly important.-

The reaction gives out heat but this is readily controllable. In'thisreactionthe bauxite and the acid combine theoretically as` but thesimultaneous intimate reaction of the salt cake further produces theacid sodium sulphate although; thesodium sulphate returns to its normalcondition in the subsequent furnace heating. Theoretically we have in.this concur# rent reaction Na2SO4+H2SO4=2NaHSO4. Any such indicatedreactions must be taken as tentative because of the preferred Vexcess ofsulphuric.

acid used in our process.

In the furnacing at the temperatures de, scribed, the reaction involvesthe distillation of the excess of the sulphuric acid from theentire massof the material during which the acid` sodium sulphate becomes normalsodium sulphate again and probably the combination be-` tween the acidsodium sulphate and the alumi-V num sulphate produces the sodiumaluminum` sulphate according to suchra reaction as term normal sodiumsulphate to distinguish from the acid form of sodium sulphate which iswritten as NaHSOl.

phate is NazSOl. This might be termed neutral sodium sulphate but incommercial worksamples What we term normal sodium sulf l of supposedlyneutral sodium sulphate often have a slight acidic reaction, althoughthey are practically all NazSOi.

the sodium sulphate is of normal character.A -Our product therefore willbe understood as represented by the formula Na2SO4Alz(SO4)3 and not Thebleaching action herein referred to' goes o'nduring this-heating of the4nfiaterial inthe fur? nace or mulfle. It is a combination between theWe therefore designate our material as sodium aluminum sulphate in which10 Y l sulphuric acid has penetrated all the particles charged from themixer and preferably allowed` to stand for a short time to make surethat the of the mixture and caused a complete chemical combination. Wethen placethis materialA ina furnace heated above 640-IE2 which is theboiling. point of pure sulphuric acid; As our upper limit we set 1418 F.which must not be exceeded as it represents the decomposition point` ofaluminum sulphate. v If the material is being handled in largequantities care must be taken not to overheat it. If there develops a.tendency to overheating the temperatureYof the furnace should bepreferably heldjustbelow avery dullred heat iii-which case suclrwould.bethe upper limit.. This is equivalent torabouti 968? F. and oncommercial. scales with 5 largepbodies of. material-it is probably thesafest working. temperature forour process. The heat- Vingtis carriedon. according to the temperature andithasze of the charge. The mixtureof the aluminumsulphate. and the sodium sulphate when heatedL and` thewater andY excesssulphuric acid drixentoffgivesus Al2Na2(SO4)4 which issodium aluminum sulphate. We have found that a 500 noundpharge canusually be heat treated in about 8 hours at which timeit will be foundtobeV a white lumpy materialwhich can be ground and sure; thatllthereactions. arecomplete.

used in the "manufacture of baking powders or other products.

A; characteristic basis ofv procedure isY as follows; With 33.3-.lbs.rofpowdered bauxite we mix 3110-.. lbs. of..v powdered salt" cake. Theseare 5to thetemperatures. employed,A the material can be withdrawn fromthe furnace', cooled and powderedaasbefore explained. l i

:We .dcninuti conne'. ourselvesiexactly `to the abcve. proportions butthey are illustratively approximate and our .process works eiciently onVsucha` basis. AWepreferably use an amount of sulphuric.4 acid. in;excess. of. the theoretical amountcnecessary. fcnordinary calculatedchemical zreactions to combine ,withthebauxite as it is.

" oui-experience thatiflwe use very. much less than,

thegabove Specified amount of sulphuric. acidthe. reactionv isaptv notto runrsatisfactorily. More thanfthegaboye-amount of theacidwould, Webve-V lieve.representawaste.A Thefexcess sulphuric acidA besidezsiaitsordinary. reactiva functionr has,r the bleaching eifect beforedescribed' and. thel resultauixprdilctvrroduced: is.. a. material of`snowy vvhitprless:V 'Ill-ie,V excessmsulphuric acid obtainedv flQJlrml?. .furnaces bY .ICQ r 1densatonis preseryed.:

and used as a byproduct for whatever purposes acid of this quality isordinarily employed.

We find that volatile impurities such as chlorides, fluorides,carbonates, organic matter. arsenic compounds and all impuritiesvolatile at the temperature employedare set free by the sulphuric acidand volatilized by the heatduring the furnacing process. As abovestated, we find it desirable to premlx the, dry ingredientsand stir theminto the acid. It is permissible to mix the sodium sulphate (or saltcake) with the sulphuric acid and then add the aluminum oxide` (orbauxite) to that mixture.

Weindicate as undesirable the addition of the aluminum. oxide.(orgbauxite) to the sulphuric acid because experience has shown thatsuch a ..mixtu1.e.ten ds to. form. a stone-like mass which is.impossible to mix, to break up or handle in a satisfactory commercialway as in a mechanical mixer.

Other variations inthe step's of the method andthe proportionsv of.:materials as before indicatedmayberesorted to within theindicated limitsVwithout departing from the-*spirit of our' invention and Willi be.readily variedby those skilledi inv calculating such proportionsyaccording to the materialsused:r and .the equipment-available. Y

What; we therefore.` claim and: desire to secure by Letters Patent is:-

1-. In. a methodmf. manufacturingsodium aluminumsulphate, those stepsconsisting in pow-- dering. a mineral sourcebf.l commercially purehydrated-oxide of. aluminum and a sodiumsulphate, in: intimately mixingYthe two: powdered mate-A rials. togethery in approximately equaliproportions ,b vweight., in. treating the powderedJ mixturewithsulphuric acid inapproximately the ratio ofl three parts by weight toone part-by weight of the hydratede oxidey of aluminumA orthe sodiumsulphate, and in subjecting. the resultant producttota sustained heat.ltreatment between approximately..l 640 F; and:1411& F.: until-theentirecharge. has. become substantially pure sodium aluminum sulphate.

2. Ina method of manufacturing-sodium aluminum. sulphate,those-.stepsconsisting in powdering a bauxiteof.1 high. purity and-asodium' sulphate, in. intimatelyl mixing the .two-powdered materialstogether in approximately equal proportions. by weight, in treatingthepowdered mixture with sulphuric acidinapproximately the ratio ofV threepartsby weight of sulphuricacid: to one. part-by. weightofeither-bauxite or sodiumJ sulphate.. and in subjecting theV resultant`product to a sustained heat'.l treatment betweeni approximately. 640. F.and .14.18 until. the entire charge has become.. sodiumaluminumsulphate.

3. In a method of manufacturing sodium aluminum sulphate, thosestepsconsisting inrpowdering bauxite -ofnhigh .purityA sodiumi sulphate,. inintimatelyemixingthe.,.two.powderedi materials together ini,approximately. equal. proportions.. by.. weight,. in..treating. the'vpowdered-i mixture .Y with an texcess e of pure. sulphuric. acid;

in` approximately theeratio of.. threeUparts-*byli weightv of sulphuric..acid .to onepart lby 'weight of.` either bauxite. or.. sodium sulphatejandi incsubf. jecting. the resultant product; to. a .sustainedfrheatxtreatment between. approximately,- 640?. F: and-i 1418iv F; untilv the.entire,4 chargefhasebecome.. sodium valuminum sulphate.

4. Ina method .of manufacturing sodiumaluminum sulphate., ;thosestepsconsistingcimmixing@ agppyvderedfmineral :sourcef commerciallypure;

